The present invention relates to a copier, facsimile, printer or similar electrophotographic image forming apparatus and, more particularly, to a developing device having a plurality of developing units arranged around a photoconductive element of a color image forming apparatus and each storing a two-component developer of particular color.
In a color image forming apparatus of the type described, developing units other than one in operation have to be brought out of contact with a photoconductive element, or image carrier, so as not to disturb a latent image and corresponding toner image formed on the drum. For this purpose, it has been customary to move the developing units other than operating one away from a developing position or to bring the magnet brush formed by a developer on each developing sleeve to an inoperative position. The problem with the former scheme is that an extra space for switching the developing units is needed to render the entire apparatus bulky. In addition, such a scheme is not practicable without complicating the switching mechanism and driving mechanism. The latter scheme does not require an extra space and is simple and useful in respect of mechanical arrangement. However, should the developer be not completely brought to the inoperative position, it would contact or adjoin the drum to disturb a latent image and corresponding toner image or deposit on the drum.